(1) Field of the Invention
The present invention relates to ganglioside-related compounds which exhibit Hanganatziu-Deicher antigen activity (referred to as "H--D antigen" hereinafter) and methods of producing the same.
The present invention also relates to ceramide-related compounds which are intermediates for synthesizing the above-described ganglioside-related compounds.
(2) Prior Art
The glycolipids of mammalian cells are the glycosidic linkages between lipid structures called ceramides in which fatty acids are amido-bonded to long-chain amino alcohols called sphingosines and sugars, such as glucose, galactose, N-acetylglucosamine, N-acetylgalactosamine, fucose, and sialic acid, in various combinations, and belong to the category of so-called sphingoglycolipids. Of these glycolipids, substances containing sialic acid are specifically called gangliosides.
H--D antigens are antigens which were discovered separately by Hanganatziu and Deicher in patients which had been injected with horse antiserums, for the purpose of curing their diseases, during the 1920s, and are known as antigens which react with the infected serums injected, as well as the red blood corpuscles of various animals such as sheep, horses, pigs, rabbits, and guinea pigs. H--D antigens have also recently been extracted as gangliosides from the red blood corpuscles of horses and have been purified to form simple molecules. In addition, it has been proven that gangliosides exhibiting H--D antigen activity are principal glycolipid components of the red blood corpuscles of horses which have been called "hematosides".
It is assumed that the chemical structure of H--D antigens is Gd Neu(2-3) Gal(1-4) Glc-Cer.
Furthermore, at present, H--D antigens have often been detected in the serum of diseased patients, regardless of whether heterologous antiserums have been administered. It has also been recognized that these antigens appear on the surfaces of cancerous lymphocyte cells of humans or domestic fowl.
Since it seems likely that H--D antigens could be used as markers, not only in the early detection of cancer, but also in immunotherapy for cancer, it is expected that they will be applied to the field of the prevention and treatment of cancer.
Most of such ganglioside-related compounds generally reside in the outer molecular layer of the two molecular layers of a cell membrane, and it is considered from the results of recent research that they play important roles in the discrimination and the acceptance and response of information in cells, in a receptor function, in differentiation, and in the proliferation, malignant change, and behavior of cells.
However, it is very difficult to isolate and purify oligosaccharide chains containing sialic acid from living bodies. It has therefore become necessary and indispensable, in order to elucidate the correlation between the accurate biological information on these oligosaccharide chains containing sialic acid and the molecular structures thereof, that these chains should be accurately synthesized.
The inventors have previously developed a method of synthesizing such a ceramide portion of a glycolipid in a stereoselective manner with a good yield (Japanese Patent Laid-Open No. 190745/1985).
When subjected to glycosylation with a sugar chain portion, the above-described ceramide (I) has conventionally been changed into a benzoylated compound (IV) by the method described below:
The compound (I) is treated with trityl chloride in pyridine to produce a tritylated compound (II) which is then treated with benzoyl chloride and dimethylaminopyridine to obtain a trityl-benzoylated compound (III). This compound is treated with para-toluenesulfonic acid to separate a trityl group and produce the benzoylated compound (IV) of the ceramide. In this series of reactions, the benzoylation can be performed without isolating the compounds (II) and (III) ((I)-(IV)).
However, the glycosylation using the above-described benzoylated compound (IV) has the disadvantages described below:
The benzoylated compound (IV) exhibits poor solubility in solvents, such as methylene chloride, benzene, or nitromethane, which are generally used for glycosylation, and thus the glycosylation can be performed only at a low concentration, and the yield of the product obtained from the glycosylation is insufficient (about 30 to 35%).